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<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE library PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN"
"../../../tools/boostbook/dtd/boostbook.dtd">
<!-- Copyright (c) 2001-2005 CrystalClear Software, Inc.
Subject to the Boost Software License, Version 1.0.
(See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
-->
<section id="date_time.examples.seconds_since_epoch">
<title>Seconds Since Epoch</title>
<para>
Example of calculating seconds elapsed since epoch (1970-Jan-1) using local_date_time.
</para>
<programlisting>
<![CDATA[
/* This example demonstrates the use of the time zone database and
* local time to calculate the number of seconds since the UTC
* time_t epoch 1970-01-01 00:00:00. Note that the selected timezone
* could be any timezone supported in the time zone database file which
* can be modified and updated as needed by the user.
*
* To solve this problem the following steps are required:
* 1) Get a timezone from the tz database for the local time
* 2) Construct a local time using the timezone
* 3) Construct a posix_time::ptime for the time_t epoch time
* 4) Convert the local_time to utc and subtract the epoch time
*
*/
#include "boost/date_time/local_time/local_time.hpp"
#include <iostream>
int main()
{
using namespace boost::gregorian;
using namespace boost::local_time;
using namespace boost::posix_time;
tz_database tz_db;
try {
tz_db.load_from_file("../data/date_time_zonespec.csv");
}catch(data_not_accessible dna) {
std::cerr << "Error with time zone data file: " << dna.what() << std::endl;
exit(EXIT_FAILURE);
}catch(bad_field_count bfc) {
std::cerr << "Error with time zone data file: " << bfc.what() << std::endl;
exit(EXIT_FAILURE);
}
time_zone_ptr nyc_tz = tz_db.time_zone_from_region("America/New_York");
date in_date(2004,10,04);
time_duration td(12,14,32);
// construct with local time value
// create not-a-date-time if invalid (eg: in dst transition)
local_date_time nyc_time(in_date,
td,
nyc_tz,
local_date_time::NOT_DATE_TIME_ON_ERROR);
std::cout << nyc_time << std::endl;
ptime time_t_epoch(date(1970,1,1));
std::cout << time_t_epoch << std::endl;
// first convert nyc_time to utc via the utc_time()
// call and subtract the ptime.
time_duration diff = nyc_time.utc_time() - time_t_epoch;
//Expected 1096906472
std::cout << "Seconds diff: " << diff.total_seconds() << std::endl;
}
]]>
</programlisting>
</section>
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